Study Evaluates Event Horse Withdrawals, Injury Risk

Dutch researchers are working to better understand exactly why event horses are withdrawn from training, conditioning, and competition and to determine if fitness tests could help predict which horses have a higher injury risk.

Photo: Stephanie L. Church, Editor-in-Chief

An upper level eventing horse galloping around a cross-country course exudes power, strength, and fitness. Unfortunately, like other high-performance horses, event horses have some risk of injury, despite owners' and riders' careful management and conditioning. But Dutch researchers are working to better understand exactly why event horses are withdrawn from training, conditioning, and competition and to determine if fitness tests could help predict which horses have a higher injury risk.

"Eventing is generally recognized as a challenging equestrian discipline, and wastage figures for this discipline seem relatively high," explained study author Carolien Munsters, PhD. "There is a need for information that provides insight into the causes of wastage and withdrawal from competition, for animal welfare and economic reasons."

Munsters and colleagues at the Utrecht University Faculty of Veterinary Medicine recently published a study in which they followed 20 horses and nine ponies selected by the Dutch national federation as they prepared to represent the nation at the European Eventing Championship in 2010 (for the ponies) and 2011 (for the horses). The research team monitored the animals' fitness levels using standardized exercise tests (SETs, one at the beginning of the season termed SET-I and another performed six weeks before the championships termed SET-II) and noted any reasons for withdrawal from the competition or preparations leading up to the event. The researchers also monitored 10 horses in each of their training sessions between the two SETs.

The researchers found that, of the equids that participated in the first SET, 45% (16/20 horses and 6/9 ponies) stopped preparing for the competition and were ultimately withdrawn before the championship due to locomotor injury. This represented a higher percentage than reported in several other studies evaluating injuries in event horses, the researchers said.

"The higher percentage of injuries here might simply have been due to lower numbers and random variation, but might also have been related to the fact that all the animals competed at the top level, yielding them more prone to injuries compared to horses of other studies which did not all compete at top level," Munsters said. "There is urgent need, with the goal of reducing injury incidence, for similar information concerning eventing animals in other countries to establish whether such high wastage percentages are universal and to better understand the effects of training methods.

Additionally, the research team learned that their study horses performed better—and thus seemed to have reached a higher fitness level—than event horses of different event levels in previous studies involving similar SETs. Still, the researchers found that two horses and eight ponies had VLA4 values—the speed at which blood lactate concentration reached 4 mmol/L, or the anaerobic threshold—below the average speed required of horses competing at that level.

Munsters said these animals should not be considered fit to compete at this level, due to their increased risk for developing rapid onset fatigue, as they have to gallop continuously above their anaerobic threshold.

The researchers also concluded that horses with better fitness parameters during SET-I were less likely to develop an injury than horses with average fitness parameters. "The field test used here showed predictive value for subsequent injuries in event horses and ponies and, thus, might aid in assessing risk factors and minimizing injuries in the future," Munsters said.

The researchers also found that the horses in the subpopulation monitored during each exercise session were schooled at "a much lower speed than required during competition," Munsters said. "An explanation for this might be that riders believe heavy conditioning training increases the risk of injury. However, insufficiently trained horses might not be physiologically adapted enough to the demands of competition," which could ultimately lead to increased injury risk.

Interestingly, the researchers said, they found that horses' heart rate during training appears to have predictive value for impending injuries.

"It was assumed that the increased heart rate observed here was an effect of the early stages of lameness, not yet detected by the rider or trainer, which seems to precede visible lameness in a horse," Munsters said. "This is an interesting observation that has not been previously described for event horses, but one that also needs confirmation in a larger population."

The researchers conceded that their study included a relatively small number of equids and suggested it should be followed up by an evaluation of a larger group. They did note, however, that it was the first study to prospectively follow a group of upper-level event horses and ponies as they prepared for a major competition.

The researchers concluded, "To prevent injuries, it is important that event horses and ponies are sufficiently fit to accommodate the physiological demands necessary for high-level competition. This study provides preliminary evidence that careful monitoring of the horses might assist in realizing this goal."

About the Author

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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